Cathodes are electron emitters used in a wide variety of vacuum tubes, such as cathode ray tubes used in televisions and various microwave tubes used in radar and communications. All of these cathodes must be kept under a high vacuum and heated to a very high temperature (>900° C.) for proper operation.
High vacuum necessitates the use of special manufacturing techniques, such as having a device that is sealed, as well as extensive baking out procedures. Further, these types of cathodes are susceptible to contamination if the cathode is ever removed from vacuum. The high vacuum thus provides a considerable constraint to tube handling, operation, and storage.
The requirement for high temperature operation poses two severe restrictions. The high temperature requires the use of special materials that can withstand the high temperature operation of the cathode. In addition, the heater reduces the energy efficiency and increases system volume, weight, and complexity.
Accordingly, there is a need for a cathode that can operate at low temperatures and have less stringent vacuum requirements, while delivering the same electron emission characteristics as conventional vacuum tube cathodes.